Valve's issue is pretty much just a lack of serious competition against Steam. They do occasionally put out something new, just at their own pace. They aren't in any rush since their core business is virtually unassailable at this point.

They have less to fear about "professional executives" worming their way in because Valve is not a publicly traded company, unlike the other examples you mentioned. It's private, Gabe Newell calls the shots at the end of the day. There's no real avenue for people to buy their way onto a board of directors and exert influence on the company from on high, or oust its historic leadership. Valve's pretty well protected from that. But it can't protect itself from sloth induced by a lack of competition.